I think the ability for custom modules to register their own products would be a really interesting idea. This way those modules can perform custom actions upon the product being bought. Here is a little example on how this could be used:
1. You're a reseller of coupon codes
2. You setup a custom product in the store with a custom module
3. When the product is bought, the module now just searches through the database of available coupons and sends an email with that coupon, removing the coupon from the database.
4. Using the "isListed" getter for a product, it can only list the product if the database has available coupons
This is just an example but I hope you get the idea. It allows to completely customize the action that gets performed when a product is bought. Allowing for a lot more customization for developers.
Already possible and is Already used by Mc server list and mcstatistics and soon NamelessHosting
They just need to register the product and make it hidden etc and save the product it
Then listen for payment details and even modify field data during checkout
Wish module creators actually make integrations like my projects but people dont know and current modules dont need it
I guess it's more or less useful for specific applications really. Not really useful for general use